The invention relates to a building block for walls, in particular retaining walls such as those used to support earthen embankments.
Earthen embankments having relatively steep slopes and heights above a meter are usually stabilized by a retaining wall. Some retaining walls are made from poured reinforced concrete, and can be labour intensive, as they require considerable preparation for concrete form work. Poured retaining walls are usually only economical where it is possible to provide large quantities of ready-mixed concrete, for example as supplied by a concrete pumping truck, which usually requires road access. In some sites, it is not convenient or possible to provide easy access for pouring concrete, and individual building blocks are used. On relatively steep, inaccessible embankments, it is important that the blocks can be man-handled easily without requiring mechanized equipment. Such blocks must be sufficiently light for one or two men to carry, e.g. about 40-80 kgs, and thus this type of block will be relatively small. Small blocks can be cemented in place, or can be supported and interconnected using reinforcing bars which serve as connecting rods which pass through appropriate openings in the blocks. Relatively low retaining walls of cemented-together building blocks are usually appropriate in relatively inaccessible areas, but difficulties have been encountered in stabilizing relatively high retaining walls of cemented-together blocks, that is walls higher than three meters. The forces incurred in retaining embankments higher than about three meters tend to become excessive, causing the wall to become unstable. It is known to provide a rearward and upward slope to such walls, termed "batter", but, this slope does not provide sufficient stability in all cases.
It is also known to provide tie back rods, concrete dowels, etc. which pass generally horizontally into an embankment and secure the retaining wall to the embankment. Such tie back rods can be either driven or augered into an embankment already in place as the wall is built up, or can be laid upon backfill material which is deposited sequentially to form the embankment as the wall is built up. While use of tie back rods of this type has, in general, been successful in stabilizing relatively high walls, difficulties have been encountered in connecting the tie rod to the wall itself. Often, steel rings or other connectors are cast or embedded into a rear face of the building block, and connect the block to the tie back rods as the wall is built. Such cast-in connectors increase the cost of the building block, and increase difficulties of installation. It can be difficult to fasten the connectors to the tie back rods as relatively close installation tolerances are required to ensure that the tie back rod and the respective connector can be connected together when installed. Clearly, the connector must be embedded sufficiently within the block to withstand restraining forces from the tie back rod. This usually requires a considerable amount of reinforcing bar embedded within the block, increasing cost and weight of the block.
Examples of building blocks for earthen embankment retaining walls are disclosed in patents as follows. U.S. Pat. No. 4,798,499 (Yamada) discloses a block or panel having an inwardly curved arch member and a straight chordal member. The chordal member is pre-stressed by a rod and thus is subjected to compression forces, and the arch member is subjected to tension. The blocks are stacked in vertical and horizontal rows without staggering or alternating of joints. Horizontal tie back members cooperate directly with joints between adjacent panels to restrain the wall against pressure from the embankment. U.S. Pat. No. 2,960,797 (Frehner) discloses a building block structure in which blocks are V-shaped or curved and are disposed in rows in which joints are staggered relative to joints of an adjacent row. Spaces between the rows can be provided to receive plants. U.S. Pat. No. 2,908,139 (Horten et al) discloses natural stone blocks reinforced by insertion of pre-stressing elements which are subjected to tension to strengthen the stone. U.S. Pat. No. 4,266,890 (Hilfiker) discloses a wall fabricated from blocks which are interconnected with vertical tie rods and horizontal tie back rods.
In many of the patents shown, it is known to stack the blocks so as to be inclined in an upwardly and a rearwardly leaning slope, and also to provide means for plants to grow between blocks, or in special recesses within the blocks. In many of the structures known to the present inventor, connections between the vertical connecting rods, or horizontal tie back rods can be difficult to assemble while the wall is being built and commonly result in stress concentrations in the block, causing premature failure of the block.
To the inventor's knowledge, no blocks have been designed in which the connecting rods used to connect horizontal rows of blocks together can be directly connected to horizontal tie back rods in the embankment.